The methods for producing a three-dimensional object layer-by-layer include, for example, selective laser sintering or melting. Here a powder-form building material is applied layer-by-layer and selectively solidified by means of laser radiation.
DE 196 49 865 C1 describes a method for producing a shaped body by layer-by-layer application and selective solidification of a metallic material powder in a process chamber. A protective gas inlet is arranged on one side of the process chamber, and on the other side a protective gas outlet. By means of these a laminar protective gas flow is generated over the applied powder in order to avoid oxidation of the surface of the materials.
DE 198 53 947 C1 describes a process chamber for the selective laser melting; in its sidewalls are arranged inlet and outlet openings for a protective gas which flows through the process chamber.
In both cases, the layer-by-layer application of the powder takes place by means of a slider, from a powder supply located upstream with respect to the protective gas flow. The powder supply and the working surface for constructing the object are located side-by-side, and accordingly the process chamber is flat and long. The protective gas flow must flow through more than half of the process chamber before it reaches the applied powder layer, as a result of which it is easy to achieve a protective gas flow that is laminar over the applied powder layer.
In devices for producing a three-dimensional object layer-by-layer, in which application of a powder layer is executed in another manner, for example from a powder supply arranged above the working surface, no such long run-in section is available for a gas flow. Here the gas flow essentially flows only across the working surface on which the object is being constructed. As a result, it is more difficult to ensure that the gas flow over the whole of the applied powder layer is laminar.
In the case of a device internally known to the applicant, a gas is guided via a channel to a sidewall of the process chamber, and is introduced into the process chamber through a perforated plate that contains a plurality of holes located side-by-side. On the other side the gas is sucked out once again. Here guide plates upstream of the perforated plate can help to improve the laminar state of the gas flow. Nevertheless a gas flow generated in this manner has irregularities and turbulences.
By the introduction of energy onto the powder that is to be solidified, spatters, smoke, gases and/or vapours can occur on the powder surface which can cause an absorption or diffraction of the laser beam. The local illumination defects that thereby result can have a negative effect on the quality of the object to be produced.
The irregularities and turbulences occurring in the device internally known to the applicant lead to a non-homogeneous removal of the smoke, gases, and/or vapours that are formed on the powder surface. By virtue of the illumination defects resulting therefrom, and as a result of turbulence occurring in the protective gas flow which can cause the powder that is to be solidified to swirl up, the quality of the object to be produced can be impaired.